Need some advice. Marriage broken down

I (37m) am now faced with a wife (33f) who has said our relationship is over (12 years 8 married). We have a great house, 2 kids under 6 amazing social life etc. But apparently for the last few years she has been unhappy and told me that from August last year she was done. The kicker, I found messages on her phone 2 days ago confirming an affair I had no idea about. What’s worse, she travelled huge distances to see him on one occasion. An occasion I helped facilitate and was excited for her trip.
We have been away on a holiday when this broke and got home last night. I am desperately trying to see if we can rebuild, despite the affair. But what is shocking me is how cold she is. Totally heartless as I am in pieces by it all. What should I be doing? I really don’t want this to end but it scares me who she is right now.
Tl;dr 8 year marriage over in wife mind. She had an affair and says she checked out a long time ago. Any way back?